Since the appearance of the Princess Leia holographic message in the 1970's Star War movie, researchers have been exploring the feasibility of producing a real world prototype. Recently, similar excitement has been stirred up in the community with the “Three Dimensional (3-D) forensic chamber” in the television series “Bones”. The closest systems that have been built so far are the Cheoptic-360 and the Holography-360, which allows a Two Dimensional (2-D) object scene to be floated in mid-air and observed by viewers from the four sides. However, it is simply the projection of a 2-D planar image, and there is no depth or disparity information as in the original object scene.
Generation of a floating image can be achieved with aerial projection. To generate a floating image, a real object is placed in an area which is generally not visible to the viewer. When illuminated, an image of the object is reflected by a beam-splitter and observable as a virtual image by the viewer, creating the impression of the object image floating in air. A background image, or a concave mirror, is sometimes added to enhance the effect. One of the significant disadvantages of this approach is the requirement of a real object.
Another method has been employed to remove the need of a real object, wherein a 2-D image of the real object is captured by a camera, and reproduced with certain display device such as a cathode ray tube (CRT) monitor, liquid crystal display (LCD) monitor, or an optical projector. The image produced by the display device is reflected by a beam-splitter and projected to the viewer as a virtual, floating image. Similarly, a background image or a concave mirror is sometimes used to provide the illusion of a 3-D effect.
The above methods and systems only provide viewers the ability to observe the floating image from a single direction. An existing product known as the “HoloCube 3D Projection Box” is based on similar principles. Recently, this has been extended to integrate two or more such aerial projection units, each projecting a floating image independently along a unique direction. The directions of projection are generally two or more of the following: front, left, right, back. An advantage of this approach is that viewers can observe the projected image from an aerial projection unit, as well as the environment behind the aerial projection unit. In this product, there is no background device or mirrors to block the sight of the viewer. Such concept has been adopted in the Cheoptic-360 system and the Holography-360 system. However, with these systems, the floating image lacks the 3-D information, such as the depth perception, and parallax is absent as the observers move their viewing positions with respect to the displayed image.
It is desirable to be able to generate a 3-D image that can be viewed from more than one vantage point, as well as providing desired depth perception and parallax information (e.g., disparity information), as opposed to conventional projection of a 2-D image onto one or more transparent screens. It is also desirable to project such a 3-D image in a less complicated and more economical manner than conventional approaches, such as the foreground/background approach (e.g., as found in Dolgoff, U.S. Pat. No. 7,492,523, “Method for displaying a three-dimensional scene”), the multi-layer display (e.g., as found in Leung et al., U.S. Pat. No. 5,745,197, “Three-dimensional real-image volumetric display system and method”; and Refai et al., U.S. Pat. No. 7,537,345, “Volumetric liquid crystal display for rendering a three-dimensional image”), and the spinning mirror (e.g., Jones et al., “Rendering for an Interactive 360° Light Field Display”, Siggraph, 2007). Further, it is desirable to be able to generate such a 3-D image without the need to use real objects as the source of the optical image.